The present invention relates to an image processing device for the detection and suppression of shadows in a camera image of a surveilled scene, the camera image optionally showing static objects with static shadow regions and moving objects with dynamic shadow regions. Image processing device includes a long-term module, which is designed to generate a long-term reference image of the surveilled scene by evaluating a long-term observation of a surveilled scene, and a mid-term module, which is designed to generate a mid-term reference image of the surveilled scene by evaluating a mid-term observation of the surveilled scene, and a related method and computer program.
Video surveillance systems are used to observe public spaces, buildings, streets, intersections, and the like with a plurality of surveillance cameras. The streams of image data recorded by the surveillance cameras are often combined in surveillance centers, where they are evaluated by surveillence personnel or in an automated manner. In the automated evaluation, it is common to use image processing algorithms that separate moving objects from a static scenery background, to track these moving objects over time, and to trigger an alarm when specified conditions are fulfilled.
Image processing algorithms of this type typically detect the moving objects by determining the difference between a current camera image and a reference image of the scene that shows the background of the surveilled scene. A known problem associated with the use of image processing systems of this type is the fact that the illumination state of the surveilled scene changes, since, in the worst case, light sources or shadows that occur are detected as moving objects. To reduce the impact of this problem, the reference image of the scene is typically updated slowly but continually, to compensate for incremental changes in the illumination state. Even when a reference image of a scene is updated, a sudden change in the illumination state, for example, such as the sun disappearing behind a cloud and then reappearing, may result in problems in the evaluation.
Publication JP 2005251132 describes a shadow detector and a method for detecting shadow regions in an image, with which, in a first step, a reference image of a scene is removed from a current camera image, so that only moving objects and shadows of these moving objects are depicted as object regions in the differential image. In a further step, the pixel intensities in the object regions are compared with the pixel intensities of the current camera image and, if certain limits are exceeded, they are classified as shadow regions or as moving objects.